After Bjorn Murray Ferris swerved into the path of an oncoming car, he said it wasn't his fault.

Instead, Ferris blamed the collision on his cousin for leaving his car keys out while Ferris was drinking.

He has since accepted responsibility for the offending, pleading guilty on Tuesday in the Whanganui District Court to driving with excess blood alcohol, dangerous driving, and driving while unlicensed.

Ferris was going through a Porirua roundabout on November 11 when he swerved into the wrong lane and "collided with the victim's vehicle", police prosecutor Sergeant Drew Morrison said.

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There were no injuries in the crash, and Ferris was found to have 111mg of alcohol in his blood. The legal limit is 50mg.

When spoken to by police, Ferris said it was his cousin's fault, and that "he should have known better than to leave the keys around after he'd been drinking", Mr Morrison said.

Defence lawyer Stephanie Burlace said the 24-year-old was sorry for his offending.

"He's extremely thankful that no one is hurt."

She said Ferris was "only released out of mental healthcare two weeks ago". Judge David Cameron remanded the matter to February 23 so police could find out how much reparation was.